import java.util.Scanner;

public class Main {
    public static int ret(int n){
        if(n==0){
            return 0;
        }
        if(n==1){
            return 1;
        }
        return ret(n-1)+ret(n-2);
    }

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int s=ret(n);
        System.out.println(s);
    }


    public static void fun(int n){
        if(n<10){
            System.out.print(n+" ");
        }
        else{

            fun(n/10);
            System.out.print(n%10+" ");
        }
    }
    public static void main2(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        fun(n);
    }



    public static int fub(int n){
        if(n==1){
            return n;
        }
        else{
            return n+fub(n-1);
        }
    }
    public static void main1(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int ret=fub(n);
        System.out.println("1~"+n+"之间的和为："+ret);
    }
}